Piecewise Linear Concordances and Isotopies

The geometrical techniques in piecewise linear topology are extended to the situation where one has a projection which must be preserved. These include general position, sunny collapsing and engulfing. They are employed to study the relative homotopy groups of the simplicial spaces of concordances and isotopies and, consequently, five a proff of a parameterized version of Hudson's concordance implies isotopy theorem.