:: deftheorem Def5 defines # MSUALG_3:def 5 :
for S being non empty non void ManySortedSign
for U1, U2 being MSAlgebra over S
for o being OperSymbol of S
for F being ManySortedFunction of U1,U2
for x being Element of Args (o,U1) st Args (o,U1) <> {} & Args (o,U2) <> {} holds
F # x = (Frege (F * (the_arity_of o))) . x;