# Homomorphism of formal group laws

From Groupprops

## Definition

Suppose and are formal group laws of dimensions and respectively. A **homomorphism** from to is a collection of power series in variables such that the following holds formally:

where and .

## Related notions

- Isomorphism of formal group laws is a homomorphism of formal group laws that has an inverse that is also a homomorphism. If an isomorphism exists between two formal group laws, then they must have the same dimension.
- Strict isomorphism of formal group laws is an isomorphism of formal group laws such that has terms of degree two and higher only.