declare fun {GetLast S}
       if S.2 == nil then S.1 else {GetLast S.2} end
end
declare fun {And c1 c2}
    if c1 then
        if c2 then
            true
        else
            false
        end
    else 
        false
    end
end
% Assemble a Beta Reduction
% B is a string that contains already done inclusions
% A is the list that needs to have I between each member
fun {B_Assemble I B A}
   {Browse [I B A]}
    if A == nil then B else {B_Assemble I {Append {Append B I} A.1} A.2} end
end
 
% Beta Reduction Main Function
% V is the variable such that \x where V = x
% E is the function expression e such that \x.e
% A is the function application expression e1 suc hthat \x.e e1
 
 
fun {Beta V E A}
    if {And (E.1 == V.1) ({GetLast E} == V.1)} then
       {B_Assemble A "" {Append {Append [""] {String.tokens E V.1} [""]}}}
    else
        if {E.1 == V.1} then
            {B_Assemble A "" {Append [""] {String.tokens E V.1}}}
        else if {GetLast E} == V.1 then  
            {B_Assemble A "" {Append {String.tokens E V.1} [""]}}
        else
            {B_Assemble A "" {String.tokens E V.1}}
        end
    end
end
 

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