Brownian motion

.PS
A: box "foo" fill 0.2; move;
B: box "moo";
arrow right at 1/4 <A.e,A.ne>;
arrow left at 1/4 <B.w,B.sw>;
.PE
 
.PS
A: box "moo" fill 0.2; move;
B: box "foo"; move;
C: box "moo";
arrow right at 0 <A.e,A.ne>;
arrow right at 1/3 <B.e,B.ne>;
arrow left at 1/3 <C.w,C.sw>;
.PE
 
.PS
A: box "moo" fill 0.2; move;
B: box "foo";
arrow right at 0 <A.e,A.ne>;
.PE
 
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