expr= '(x1 & x2 | x3) == ( (x1 & x2 ) | x3)'; /// \sleftarrow{\normalfont expression is true ?}
n=size(strindex(expr,'x'),'*')  /// \sleftarrow {\begin{minipage}[t]{6cm}{\nf{}number of occurence of \verb+'x'+ in string\\ \verb+expr+.  \verb+size+ with option \verb+'*'+ returns product of matrix dimensions} \end{minipage}}
nv=0;
for i=1:n 
  if grep(expr,'x'+string(i))<>[] then /// \sleftarrow{\normalfont are \verb+x1,x2,...+ present in  \verb+expr+ ?}
    nv=nv+1;
  end
end
nv /// \sleftarrow{\normalfont number of \verb+xi+ variables in  \verb+expr+ }

for i=1:nv
  expr=strsubst(expr,'x'+string(i),'x(:,'+string(i)+')'); 
end

expr   /// \sleftarrow{\normalfont substitution of  \verb+xi+ by \verb+x(:,i)+ in \verb+expr+ {for} \verb+i=1:nv+}
n=nv ;  /// \sleftarrow{\normalfont \verb+n+ is the number of \verb+xi+ variables occuring in  \verb+expr+}

T=[1;0];
x=ones(2^n,n);
for i=1:n 
  x(:,i) = ones(2^(i-1),1).*.(T.*.ones(2^(n-i),1));
end
x = (x > 0)  /// \sleftarrow{\normalfont a matrix giving all the possible boolean values {for} \verb+n+ variables }

execstr('rep=('+expr+')');  /// \sleftarrow {\begin{minipage}[t]{6cm}{\nf{}all the possible values {for} \verb+expr+ (we build a Scilab expressions and call the interpreter to evaluate it)} \end{minipage}}

and(rep)  /// \sleftarrow{\normalfont is \verb+expr+ always true ? all the entries of \verb+rep+ must be true }