The algebraic difficulty of determining the component values in a circuit of known topology and specifications is large. Expert circuit designers use terminal equivalence and power arguments to reduce the apparent synergy in a circuit so that their computational power can be focussed. A new descriptive mechanism, called slices, is introduced. Slices combine the notion of equivalence with identification of parameters. Armed with appropriate slices, an automatic analysis procedure, Analysis by Propagation of Constraints can be used to assign the component values in a circuit. Techniques of formation, notation, and use of slices are described. The origin of slices in the topological design process is indicated. Slices are shown to be of wider interest in scientific thought than just in circuit analysis.