  In this paper I introduce modular symbols for Maass wave cusp forms. They
appear in the guise of finitely additive functions on the Boolean algebra
generated by intervals with non--positive rational ends, with values in
analytic functions (pseudo--measures in the sense of [MaMar2]). After
explaining the basic issues and analogies in the extended Introduction, I
construct modular symbols in the sec. 1 and the related L\'evy--Mellin
transforms in the sec. 2. The whole paper is an extended footnote to the
Lewis--Zagier fundamental study [LZ2].
