reserve x,y for set;
reserve C,C9,D,D9,E for non empty set;
reserve c for Element of C;
reserve c9 for Element of C9;
reserve d,d1,d2,d3,d4,e for Element of D;
reserve d9 for Element of D9;
reserve i,j for natural Number;
reserve F for Function of [:D,D9:],E;
reserve p,q for FinSequence of D,
  p9,q9 for FinSequence of D9;
reserve f,f9 for Function of C,D,
  h for Function of D,E;
reserve T,T1,T2,T3 for Tuple of i,D;
reserve T9 for Tuple of i, D9;
reserve S for Tuple of j, D;
reserve S9 for Tuple of j, D9;
reserve F,G for BinOp of D;
reserve u for UnOp of D;
reserve H for BinOp of E;

theorem Th25:
  F is associative implies F[:](id D,d)*(F.:(f,f9)) = F.:(f,F[:](id D,d)*f9)
proof
  assume
A1: F is associative;
  now
    let c;
    thus (F[:](id D,d)*(F.:(f,f9))).c = (F[:](id D,d)).((F.:(f,f9)).c) by
FUNCT_2:15
      .= (F[:](id D,d)).(F.(f.c,f9.c)) by FUNCOP_1:37
      .= F.((id D).(F.(f.c,f9.c)),d) by FUNCOP_1:48
      .= F.(F.(f.c,f9.c),d)
      .= F.(f.c,F.(f9.c,d)) by A1
      .= F.(f.c,(F[:](f9,d)).c) by FUNCOP_1:48
      .= F.(f.c,((F[:](id D,d))*f9).c) by FUNCOP_1:50
      .= (F.:(f,F[:](id D,d)*f9)).c by FUNCOP_1:37;
  end;
  hence thesis by FUNCT_2:63;
end;
