A Course In Universal Algebra, Burris, Sankappanavar
〔A Course In Universal Algebra by Stanley N Burris, H P Sankappanavar. At http://www.math.uwaterloo.ca/~snburris/htdocs/ualg.html〕
〔A Course In Universal Algebra by Stanley N Burris, H P Sankappanavar. At http://www.math.uwaterloo.ca/~snburris/htdocs/ualg.html〕