ClassCastException

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```
java.lang.ClassCastException: class org.arend.term.concrete.Concrete$AppExpression cannot be cast to class org.arend.term.concrete.Concrete$LamExpression (org.arend.term.concrete.Concrete$AppExpression and org.arend.term.concrete.Concrete$LamExpression are in unnamed module of loader com.intellij.ide.plugins.cl.PluginClassLoader @33326218)
at org.arend.typechecking.visitor.DefinitionTypechecker.typecheckClass(DefinitionTypechecker.java:2971)
at org.arend.typechecking.visitor.DefinitionTypechecker.visitClass(DefinitionTypechecker.java:232)
at org.arend.typechecking.visitor.DefinitionTypechecker.visitClass(DefinitionTypechecker.java:64)
at org.arend.term.concrete.Concrete$ClassDefinition.accept(Concrete.java:2160)
at org.arend.term.concrete.Concrete$Definition.accept(Concrete.java:2100)
at org.arend.actions.ArendShowTypeAction.doInvoke(ArendShowTypeAction.kt:85)
at org.arend.actions.ArendShowTypeAction.access$doInvoke(ArendShowTypeAction.kt:37)
at org.arend.actions.ArendShowTypeAction$getHandler$1.invoke(ArendShowTypeAction.kt:45)
at com.intellij.codeInsight.actions.CodeInsightAction.lambda$actionPerformedImpl$0(CodeInsightAction.java:67)
at com.intellij.codeInsight.actions.CodeInsightAction.lambda$actionPerformedImpl$1(CodeInsightAction.java:73)
at com.intellij.openapi.command.impl.CoreCommandProcessor.executeCommand(CoreCommandProcessor.java:225)
at com.intellij.openapi.command.impl.CoreCommandProcessor.executeCommand(CoreCommandProcessor.java:177)
at com.intellij.openapi.command.impl.CoreCommandProcessor.executeCommand(CoreCommandProcessor.java:158)
at com.intellij.codeInsight.actions.CodeInsightAction.actionPerformedImpl(CodeInsightAction.java:64)
at com.intellij.codeInsight.actions.CodeInsightAction.actionPerformed(CodeInsightAction.java:40)
at com.intellij.openapi.actionSystem.ex.ActionUtil.doPerformActionOrShowPopup(ActionUtil.kt:305)
at com.intellij.openapi.keymap.impl.ActionProcessor.performAction(ActionProcessor.java:32)
at com.intellij.openapi.keymap.impl.IdeKeyEventDispatcher$actionProcessor$1.performAction(IdeKeyEventDispatcher.kt:495)
at com.intellij.openapi.keymap.impl.IdeKeyEventDispatcherKt.doPerformActionInner$lambda$4$lambda$3(IdeKeyEventDispatcher.kt:844)
at com.intellij.openapi.application.TransactionGuardImpl.performActivity(TransactionGuardImpl.java:106)
at com.intellij.openapi.application.TransactionGuardImpl.performUserActivity(TransactionGuardImpl.java:95)
at com.intellij.openapi.keymap.impl.IdeKeyEventDispatcherKt.doPerformActionInner$lambda$4(IdeKeyEventDispatcher.kt:844)
at com.intellij.openapi.actionSystem.impl.ActionManagerImpl.performWithActionCallbacks(ActionManagerImpl.kt:1161)
at com.intellij.openapi.actionSystem.ex.ActionUtil.performDumbAwareWithCallbacks(ActionUtil.kt:322)
at com.intellij.openapi.keymap.impl.IdeKeyEventDispatcherKt.doPerformActionInner(IdeKeyEventDispatcher.kt:842)
at com.intellij.openapi.keymap.impl.IdeKeyEventDispatcherKt.access$doPerformActionInner(IdeKeyEventDispatcher.kt:1)
at com.intellij.openapi.keymap.impl.IdeKeyEventDispatcher.processAction$intellij_platform_ide_impl(IdeKeyEventDispatcher.kt:571)
at com.intellij.openapi.keymap.impl.IdeKeyEventDispatcher.processAction(IdeKeyEventDispatcher.kt:508)
at com.intellij.openapi.keymap.impl.IdeKeyEventDispatcher.processActionOrWaitSecondStroke(IdeKeyEventDispatcher.kt:447)
at com.intellij.openapi.keymap.impl.IdeKeyEventDispatcher.inInitState(IdeKeyEventDispatcher.kt:440)
at com.intellij.openapi.keymap.impl.IdeKeyEventDispatcher.dispatchKeyEvent(IdeKeyEventDispatcher.kt:302)
at com.intellij.ide.IdeEventQueue.dispatchKeyEvent(IdeEventQueue.kt:622)
at com.intellij.ide.IdeEventQueue._dispatchEvent$lambda$11(IdeEventQueue.kt:585)
at com.intellij.openapi.application.impl.RwLockHolder.runWithEnabledImplicitRead(RwLockHolder.kt:138)
at com.intellij.openapi.application.impl.RwLockHolder.runWithImplicitRead(RwLockHolder.kt:129)
at com.intellij.ide.IdeEventQueue._dispatchEvent(IdeEventQueue.kt:585)
at com.intellij.ide.IdeEventQueue.access$_dispatchEvent(IdeEventQueue.kt:77)
at com.intellij.ide.IdeEventQueue$dispatchEvent$processEventRunnable$1$1$1.compute(IdeEventQueue.kt:362)
at com.intellij.ide.IdeEventQueue$dispatchEvent$processEventRunnable$1$1$1.compute(IdeEventQueue.kt:361)
at com.intellij.openapi.progress.impl.CoreProgressManager.computePrioritized(CoreProgressManager.java:843)
at com.intellij.ide.IdeEventQueue$dispatchEvent$processEventRunnable$1$1.invoke(IdeEventQueue.kt:361)
at com.intellij.ide.IdeEventQueue$dispatchEvent$processEventRunnable$1$1.invoke(IdeEventQueue.kt:356)
at com.intellij.ide.IdeEventQueueKt.performActivity$lambda$1(IdeEventQueue.kt:1021)
at com.intellij.openapi.application.TransactionGuardImpl.performActivity(TransactionGuardImpl.java:114)
at com.intellij.ide.IdeEventQueueKt.performActivity(IdeEventQueue.kt:1021)
at com.intellij.ide.IdeEventQueue.dispatchEvent$lambda$7(IdeEventQueue.kt:356)
at com.intellij.openapi.application.impl.RwLockHolder.runIntendedWriteActionOnCurrentThread(RwLockHolder.kt:209)
at com.intellij.openapi.application.impl.ApplicationImpl.runIntendedWriteActionOnCurrentThread(ApplicationImpl.java:830)
at com.intellij.ide.IdeEventQueue.dispatchEvent(IdeEventQueue.kt:398)
at java.desktop/java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:207)
at java.desktop/java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:128)
at java.desktop/java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:117)
at java.desktop/java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:113)
at java.desktop/java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:105)
at java.desktop/java.awt.EventDispatchThread.run(EventDispatchThread.java:92)
```
`Ctrl+Shift+P` on `byLeft`

Reproduce the failure by invoking Ctrl+Shift+P on `byLeft`, then inspect `DefinitionTypechecker.java:2971` and the `ArendShowTypeAction.kt:85` call path. Trace why the expression at that point is an `AppExpression` rather than a `LamExpression`; done means the action no longer raises this `ClassCastException` for the reported case.

Written by the indexing model from the issue text.