SpectralSequencePageMap -- the type of all spectral sequence page maps

A (homological, or lower index) spectral sequence page map consists of:

1. A fixed integer r ≥0 , the page number;

2. A collection of homomorphisms {d^r_p,q: E^r_p,q →E^r_p-r,q+r-1} for p,q ∈ℤ, r ≥0 such that d^r_p,q d^r_p+r,q-r+1 = 0.

Alternatively a (cohomological, or upper index) spectral sequence page consists of:

1’. A fixed integer r ≥0, the page number;

2’. A collection of homomorphisms {d_r^p,q: E_r^p,q →E_r^p+r,q-r+1} for p,q ∈ℤ, r ≥0 such that d_r^p,q d_r^p-r,q+r-1 = 0.

The type SpectralSequencePageMap is a data type for working with spectral sequences and the differentials on the pages of a spectral sequence.