let V be RealLinearSpace; :: thesis: for u, u1, u2, v, v1, v2, w, w1, x, y being VECTOR of V st Gen x,y & u,u1,v,v1 are_COrte_wrt x,y & w,w1,v,v1 are_COrte_wrt x,y & w,w1,u2,v2 are_COrte_wrt x,y & not w = w1 & not v = v1 holds
u,u1,u2,v2 are_COrte_wrt x,y

let u, u1, u2, v, v1, v2, w, w1, x, y be VECTOR of V; :: thesis: ( Gen x,y & u,u1,v,v1 are_COrte_wrt x,y & w,w1,v,v1 are_COrte_wrt x,y & w,w1,u2,v2 are_COrte_wrt x,y & not w = w1 & not v = v1 implies u,u1,u2,v2 are_COrte_wrt x,y )
assume A1: Gen x,y ; :: thesis: ( not u,u1,v,v1 are_COrte_wrt x,y or not w,w1,v,v1 are_COrte_wrt x,y or not w,w1,u2,v2 are_COrte_wrt x,y or w = w1 or v = v1 or u,u1,u2,v2 are_COrte_wrt x,y )
assume that
A2: u,u1,v,v1 are_COrte_wrt x,y and
A3: w,w1,v,v1 are_COrte_wrt x,y and
A4: w,w1,u2,v2 are_COrte_wrt x,y ; :: thesis: ( w = w1 or v = v1 or u,u1,u2,v2 are_COrte_wrt x,y )
Orte (x,y,u), Orte (x,y,u1) // v,v1 by A2;
then A5: v,v1 // Orte (x,y,u), Orte (x,y,u1) by ANALOAF:12;
Orte (x,y,w), Orte (x,y,w1) // v,v1 by A3;
then A6: v,v1 // Orte (x,y,w), Orte (x,y,w1) by ANALOAF:12;
A7: Orte (x,y,w), Orte (x,y,w1) // u2,v2 by A4;
now :: thesis: ( w <> w1 & v <> v1 implies u,u1,u2,v2 are_COrte_wrt x,y )
assume that
A8: w <> w1 and
A9: v <> v1 ; :: thesis: u,u1,u2,v2 are_COrte_wrt x,y
Orte (x,y,w), Orte (x,y,w1) // Orte (x,y,u), Orte (x,y,u1) by ;
then Orte (x,y,u), Orte (x,y,u1) // u2,v2 by ;
hence u,u1,u2,v2 are_COrte_wrt x,y ; :: thesis: verum
end;
hence ( w = w1 or v = v1 or u,u1,u2,v2 are_COrte_wrt x,y ) ; :: thesis: verum