Order affine completeness of lattices with Boolean congruence lattices

This paper grew out from attempts to determine which modular lattices of finite height are locally order affine complete. A surprising discovery was that one can go quite far without assuming the modularity itself. The only thing which matters is that the congruence lattice is finite Boolean. The local order affine completeness problem of such lattices L easily reduces to the case when L is a subdirect product of two simple lattices L ₁ and L ₂. Our main result claims that such a lattice is locally order affine complete iff L ₁ and L ₂ are tolerance trivial and one of the following three cases occurs:

1)	L = L 1 × L 2
2)	L is a maximal sublattice of the direct product
3)	L is the intersection of two maximal sublattices, one containing 〈0, 1〉 and the other 〈1, 0〉.

Research supported by the Estonian Science Foundation grant number 5368.