read MultiAlmkvistZeilberger:

print(MAZ(1,
((t1-t2)*(t1-t3)*(t2-t3))^(2*z)*
((1-t1)*(1-t2)*(1-t3))^y,t1*t2*t3,[t1,t2,t3],x,X,{y,z}));

time();

quit: