No terriers wander among the signs of the zodiac.
Nothing that does not wander among the signs of the zodiac is a comet.
Nothing but a terrier has a curly tail.
No comet has a curly tail.

The following sorites are taken from Lewis Carroll’s Symbolic Logic. All are valid. Rewrite each sorites in standard form, using letters to represent the terms and reducing the number of terms whenever necessary. Then use Venn diagrams or the rules method to prove each one valid.