\coordinate (A) at (-1, 1);
\coordinate (B) at ( 1, 1);
\coordinate (C) at ( 1,-1);
\coordinate (D) at (-1,-1);


\filldraw  (A) circle (1pt);
\filldraw  (B) circle (1pt);
\filldraw  (C) circle (1pt);
\filldraw  (D) circle (1pt);


\node at ($(A)+(-0.2,0.2)$) {\small{$A$}};
\node at ($(B)+( 0.2,0.2)$) {\small{$B$}};
\node at ($(C)+( 0.2,-0.2)$) {\small{$C$}};
\node at ($(D)+(-0.2,-0.2)$) {\small{$D$}};


%Convex combinations parameters
\pgfmathparse{0.05} \let\t\pgfmathresult;
\pgfmathparse{1-\t} \let\tt\pgfmathresult;

\pgfmathparse{0.95} \let\s\pgfmathresult;
\pgfmathparse{1-\s} \let\ss\pgfmathresult;

\draw [thick] ($\t*(A)+\tt*(B)$) -- ($\s*(A)+\ss*(B)$);
\draw [thick] ($\t*(B)+\tt*(C)$) -- ($\s*(B)+\ss*(C)$);
\draw [thick] ($\t*(C)+\tt*(D)$) -- ($\s*(C)+\ss*(D)$);
\draw [thick] ($\t*(D)+\tt*(A)$) -- ($\s*(D)+\ss*(A)$);


\draw [thick] ($\t*(A)+\tt*(C)$) -- ($\s*(A)+\ss*(C)$);
\draw [thick] ($\t*(B)+\tt*(D)$) -- ($\s*(B)+\ss*(D)$);
