The linear piecewise lexicographic programming (LPWLGP) problem is a mathem
atical programming model with linear constraints and piecewise linear objec
tive functions, arranged in a lexicographic hierarchy. Lexicographic spaces
are introduced, and the differential properties of functions taking values
in them are discussed. Necessary and sufficient optimality conditions for
the LPWLGP problem are derived, and an algorithm based on them is formulate
d.