(* Package for Clifford Algebra in 4-dimensional Minkowski positive (-+++), Minkowski negative (+---), Euclidean (++++) and anti-Euclidean (----) spaces. We will give the elements a standard grade-structured representation in the form shown in the following examples: e12={0,z4,{z3,{0,0,1}},z4,0} e0={0,{1,z3},z6,z4,0} where z3,z4,z6 stand for lists of 3,4,6 zeros. Author: Josep Manel Parra Serra Address: Departament de Fisica Fonamental Universitat de Barcelona Diagonal 647 E-08028 Barcelona (Spain) e-mail: jmparra@hermes.ffn.ub.es FAX: 34 3 402 11 49 *) <