On spaces in which lindelo"f sets are closed

الملخص EN

A topological space X is said to be L-closed if every lindelo"f subset of X is closed.

We introduce the notion of lindelo^f sets are closed and study it properties.

Various results are obtained analogous to those of algebraic topology.

However, there are differences because lindelo"f spaces are not compactness.

Some algebraic results are obtained from the topology, and the interactions between the algebra and the topology are studied.