Requirements vs Specification

The distinction between the two, Requirements vs Specification, can be subtle at times.
Both may run the risk of containing incompatibilities and inconsistencies that need to be teased out through various means.
An to approach the challenge of making sense of requirements, and making requirements sensible is to create a compatibility matrix.

So as an exercise - assess the interdependencies and linkages (positive and negative) between the Good Friday Agreement (GFA) and the proposed replacement for 'backstop' previously agreed as part of the the UK-EU Withdrawal Agreement (WA).
The following requirements can be used for this exercise

1. To protect the GFA the signatories require:
1. There must be no hard border between Ireland and Northern Ireland
2. Within a customs territory there can be no tariffs, quotas, or checks on rules of origin.
3. The Common Travel Area arrangements between Ireland and the United Kingdom must remain.
4. There must be a Single Electricity Energy Market on the island of Ireland.
5. North-South cooperation and the all-island economy must be protected.
6. Regulation will remained aligned to preserve the EU's Single Market and covering: legislation on goods, sanitary rules for veterinary controls (“SPS rules”), rules on agricultural production/marketing, VAT and excise in respect of goods, and state aid rules.
2. To enable an independent UK Trade Policy on withdrawal from the EU HMG require:
1. Border checks in and out of the territory of the UK.
2. To restore the UK Supreme Court to the court of last resort for the UK (the highest judicial body within a jurisdiction).
3. To apply UK's own customs tariffs for goods entering the UK market.
4. To establish UK's own goods rules, legal compliance regulation and checks.
5. To have UK Govt. only controlled internal goods market.
6. To have UK Govt. only controlled services market.
7. To have UK Govt. only controlled labour market.
8. To have UK Govt. only controlled immigration policy (movement of people).
9. To restore UK Govt. only controlled maritime resources.
10. To apply UK's own independently determined Customs Tariffs.
11. To enable UK's own approach to industry supports and subsidies (may be subject to WTO competition rules).
12. To negotiate and establish UK's own trade deals with 3rd countries.

Partially completed feature requirements matrix for Brexit (+/- correlation, o=no or unknown effect)

WA - proposed protocol on Ireland/Northern Ireland
https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/836029/PM_letter_to_Juncker.pdf
... and a decoding of the letter
https://www.politico.eu/article/boris-johnson-big-brexit-offer-decoded-annotated/

The GFA (only 35 pages)
https://www.dfa.ie/media/dfa/alldfawebsitemedia/ourrolesandpolicies/northernireland/good-friday-agreement.pdf

European Commission notes on Brexit
https://ec.europa.eu/ireland/news/key-eu-policy-areas/brexit_en