\def\longleftarrow{\leftarrow\kern-11mu\lyxbar}
\def\Longrightarrow{\lyxeq\kern-9.5mu\Rightarrow}
\def\Longleftarrow{\Leftarrow\kern-9.5mu\lyxeq}
\def\longleftarrow{\leftarrow\kern-11mu\lyxbar}
\def\Longrightarrow{\lyxeq\kern-9.5mu\Rightarrow}
\def\Longleftarrow{\Leftarrow\kern-9.5mu\lyxeq}