take IT = [*(+ (x1,y1)),(+ (x2,y2))*]; :: thesis: ex x1, x2, y1, y2 being Element of REAL st

( x = [*x1,x2*] & y = [*y1,y2*] & IT = [*(+ (x1,y1)),(+ (x2,y2))*] )

thus ex x1, x2, y1, y2 being Element of REAL st

( x = [*x1,x2*] & y = [*y1,y2*] & IT = [*(+ (x1,y1)),(+ (x2,y2))*] ) by A1, A2; :: thesis: verum

( x = [*x1,x2*] & y = [*y1,y2*] & IT = [*(+ (x1,y1)),(+ (x2,y2))*] )

thus ex x1, x2, y1, y2 being Element of REAL st

( x = [*x1,x2*] & y = [*y1,y2*] & IT = [*(+ (x1,y1)),(+ (x2,y2))*] ) by A1, A2; :: thesis: verum