?-
select(spj,[[sno,'=',"S1"]],t51),
project(t51,[pno],t52),
project(projects,[jno],t53),
times(t52,t53,t54),
project(spj,[pno,jno],t55),
minus(t54,t55,t56),
project(t56,[jno],t57),
project(projects,[jno],t58),
minus(t58,t57,t59),
displayRelation(t59).
