Just because I know that you enjoy having your head spin, Dr Bill ~

There are several different types of estoppel. Here are the major variations under Michigan law.

Collateral estoppel - Generally, collateral estoppel precludes relitigation of an issue if a question of fact essential to the judgment was actually litigated and determined by a valid and final judgment, the same parties had a full opportunity to litigate the issue, and there is mutuality of estoppel.

Equitable estoppel - Equitable estoppel can arise when: (1) a party, by representations, admissions, or silence, intentionally or negligently induces another party to believe facts; (2) the other party justifiably relies and acts on that belief; and (3) the other party would be prejudiced if the first party were allowed to deny the existence of those facts.

Promissory estoppel - To establish a claim based on promissory estoppel, there must be: (1) a promise; (2) that the promisor should reasonably have expected to induce action of a definite and substantial character on the part of the promisee; (3) which in fact produced reliance or forbearance of that nature; and (4) in circumstances such that the promise must be enforced if injustice is to be avoided.

You can read about cases involving estoppel here:

http://courtofappeals.mijud.net/Digest/topiclists/Estoppel_pg1.htm