Seems like AYBABTME is talking about constrained optimization, whereas you are speaking of "constraints" in a different context, i.e., this paper (https://dspac

Seems like AYBABTME is talking about constrained optimization, whereas you are speaking of "constraints" in a different context, i.e., this paper (https://dspace.mit.edu/handle/1721.1/6255 https://dspace.mit.edu/handle/1721.1/6255) by Stallman and Sussman, further developed in Guy Steele's PhD dissertation, eventually leading to the propagator model by Radul and Sussman (https://groups.csail.mit.edu/mac/users/gjs/propagators/ https://groups.csail.mit.edu/mac/users/gjs/propagators/). Both kinds of "constraints" are very interesting, but one is a class of numerical algorithms and another a general programming framework.