Definition coin1 (sc : col_squares) : colors := sc c1.
Definition coin2 (sc : col_squares) : colors := sc c2.
Definition coin3 (sc : col_squares) : colors := sc c3.

Lemma F_Sh :
'Fix_to[sh] = [set x | (coin0 x == coin1 x) && (coin2 x == coin3 x)].