reserve x,y,c for set;

theorem Th6:
  x in the carrier of BorrowStr(x,y,c) & y in the carrier of
  BorrowStr(x,y,c) & c in the carrier of BorrowStr(x,y,c)
proof
  c in the carrier of 1GateCircStr(<*x,c*>,and2a) by FACIRC_1:43;
  then
A1: c in the carrier of BorrowIStr(x,y,c) by FACIRC_1:20;
  y in the carrier of 1GateCircStr(<*x,y*>,and2a) by FACIRC_1:43;
  then y in the carrier of 1GateCircStr(<*x,y*>,and2a)+*1GateCircStr(<*y,c*>,
  and2) by FACIRC_1:20;
  then
A2: y in the carrier of BorrowIStr(x,y,c) by FACIRC_1:20;
  x in the carrier of 1GateCircStr(<*x,c*>,and2a) by FACIRC_1:43;
  then x in the carrier of BorrowIStr(x,y,c) by FACIRC_1:20;
  hence thesis by A2,A1,FACIRC_1:20;
end;
