Let S , T be non empty posets, g be a map from S into T , and d be a map from T into S . Let S , T be non empty posets, g be a map from S into T , and d be a map from T into S . Let L be a non empty relational structure and let p be a map from L into L . We introduce p is a projection operator as a synonym of p is projection. Let L be a non empty relational structure.
L is projection.
Let L be a non empty relational structure. Observe that there exists a map from L into L which is projection. Let L be a non empty relational structure and let c be a map from L into L . We introduce c is a closure operator as a synonym of c is closure. Let L be a non empty relational structure.