Expressionse,b,f,aβ·=xVariableβ£xβbAbstractionβ£fβaApplicationVariablesxβk,x,y,β¦Numbersnβ0,1,2,β¦ \small\begin{array}{lrcll} \mathrm{Expressions}\quad & e,b,f,a & {\Coloneqq} & x & \quad\mathrm{Variable} \\ & & {\mid} & x\Rightarrow b & \quad\mathrm{Abstraction} \\ & & {\mid} & f\leftarrow a & \quad\mathrm{Application} \\ \mathrm{Variables} & x ...