let D be non empty set ; :: thesis: for d being Element of D
for i being natural Number
for T1, T2 being Tuple of i,D
for F being BinOp of D st F is associative holds
(F [;] (d,(id D))) * (F .: (T1,T2)) = F .: (((F [;] (d,(id D))) * T1),T2)

let d be Element of D; :: thesis: for i being natural Number
for T1, T2 being Tuple of i,D
for F being BinOp of D st F is associative holds
(F [;] (d,(id D))) * (F .: (T1,T2)) = F .: (((F [;] (d,(id D))) * T1),T2)

let i be natural Number ; :: thesis: for T1, T2 being Tuple of i,D
for F being BinOp of D st F is associative holds
(F [;] (d,(id D))) * (F .: (T1,T2)) = F .: (((F [;] (d,(id D))) * T1),T2)

let T1, T2 be Tuple of i,D; :: thesis: for F being BinOp of D st F is associative holds
(F [;] (d,(id D))) * (F .: (T1,T2)) = F .: (((F [;] (d,(id D))) * T1),T2)

let F be BinOp of D; :: thesis: ( F is associative implies (F [;] (d,(id D))) * (F .: (T1,T2)) = F .: (((F [;] (d,(id D))) * T1),T2) )
assume A1: F is associative ; :: thesis: (F [;] (d,(id D))) * (F .: (T1,T2)) = F .: (((F [;] (d,(id D))) * T1),T2)
per cases ( i = 0 or i <> 0 ) ;
suppose A2: i = 0 ; :: thesis: (F [;] (d,(id D))) * (F .: (T1,T2)) = F .: (((F [;] (d,(id D))) * T1),T2)
then F .: (T1,T2) = <*> D by Lm1;
then A3: (F [;] (d,(id D))) * (F .: (T1,T2)) = <*> D ;
T2 = <*> D by A2;
hence (F [;] (d,(id D))) * (F .: (T1,T2)) = F .: (((F [;] (d,(id D))) * T1),T2) by ; :: thesis: verum
end;
suppose i <> 0 ; :: thesis: (F [;] (d,(id D))) * (F .: (T1,T2)) = F .: (((F [;] (d,(id D))) * T1),T2)
then reconsider C = Seg i as non empty set ;
( T1 is Function of C,D & T2 is Function of C,D ) by Lm4;
hence (F [;] (d,(id D))) * (F .: (T1,T2)) = F .: (((F [;] (d,(id D))) * T1),T2) by ; :: thesis: verum
end;
end;