Syntax for Piecewise?

What would be a good syntax for piecewise-defined function? Currently, it's
- `Piecewise(a provided b, c provided d)` without the otherwise case
- `Piecewise(a provided b, c provided d, e)` with the otherwise case.

By this time, multiple ideas have been considered:
- `a if b else c` (but how to expand for more than two cases?)
- `(a if b, c if d, ..., e)` (but will there be no conflicts in the future?)
- `(a if b else c if d else ..., e)` (is it readable enough?)
- `piecewise((a, b), (c, d), ..., e)` (sympy's way)
- `if a then b elif c then d ... else e` (is it convenient?)

Your ideas are welcomed

Start by reviewing the current Piecewise syntax described in the issue and the alternative forms under consideration. Compare how each option would represent multiple conditions and an otherwise case; done means the project has selected and documented a syntax to implement.

Written by the indexing model from the issue text.