Non matching meshes

Is there a way to handle non-matching meshes (with no overlaps) with freefem. I have a very basic laplacian test case, two squares meshed independly but sharing a common boundary (same tag). I read that mortar method could do the job using lagrangian multiplier to enforce continuity condition \int_{\Gamma}(u_1-u_2)=0, where u_i are the restriction of u on each side of the border but i can’t see how to do that… Any idea ?

best reragds.

PS : it’s a classical lapacian with u=0 on Gamma tag=1 and u=1 Gamma tag=2, dn(u)=0 on Gamma tag 3.
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