1 | initial version |

The substitution needs to happen in each coefficient.

The following works.

```
sage: E.<x,y> = ExteriorAlgebra(SR)
sage: _ = var('t')
sage: theta = 3*x+t*y
sage: print "theta =", theta
theta = 3*x + t*y
sage: theta.map_coefficients(lambda x: x.substitute({t:0}))
3*x
```

2 | No.2 Revision |

The substitution needs to happen in each coefficient.

The following works.

```
sage: E.<x,y> = ExteriorAlgebra(SR)
sage: _ = var('t')
sage: theta = 3*x+t*y
sage: print "theta =", theta
theta = 3*x + t*y
sage: theta.map_coefficients(lambda
```~~x: x.substitute({t:0}))
~~c: c.substitute({t:0}))
3*x

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