To represent a negative cause-and-effect arc, a downward pointing triangle is used instead of an upward pointing triangle. Thus the sequence of shapes below correspond to the following flow graph and set of equations.

I = I - (X * the percent overlap)

O = O + (X * the percent overlap)

X = C3 / I

where C3 is a global constant.

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Rules for two squares

Rules for upward pointing triangles

Rules for triangles overlapping with only one square and for multiple overlapping triangles