It is possible to append an arbitary number of quote symbols
at the end of an prefix/infix/mixfix operator:
applied form standalone form
-' 42 (-'_)
x +' y (+')
a' <- 1 ('<-)
Pretty-printing will use the quote symbols for disambiguation.
The derived symbols can be produced by Why3 by appending
a suffix of the form "_toto" or "'toto". These symbols can
be parsed/printed as "(+)_toto" or "(+)'toto", respectively.