Composite field (mathematics)

A composite field is an object of study in field theory. Let L be a field, and let F, K be subfields of L. Then the (internal) composite of F and K is defined to be the intersection of all subfields of L containing both F and K. The composite is commonly denoted FK. When F and K are not regarded as subfields of a common field then the (external) composite is defined using the tensor product of fields.