\def\longleftarrow{\leftarrow\kern-11mu\lyxbar}
\def\Longrightarrow{\lyxeq\kern-9.5mu\Rightarrow}
\def\Longleftarrow{\Leftarrow\kern-9.5mu\lyxeq}
-\def\implies{\Longrightarrow}
+\def\implies{\Longrightarrow} amsmath
\def\mapsto{\mapstochar\kern-9mu\rightarrow}
\def\longmapsto{\mapstochar\kern-6mu\lyxbar\kern-11mu\rightarrow}
\def\models{\vert\kern-7mu\lyxeq}