{"action":"opened","issue":{"url":"https://api.github.com/repos/jccriado/matchingtools/issues/25","repository_url":"https://api.github.com/repos/jccriado/matchingtools","labels_url":"https://api.github.com/repos/jccriado/matchingtools/issues/25/labels{/name}","comments_url":"https://api.github.com/repos/jccriado/matchingtools/issues/25/comments","events_url":"https://api.github.com/repos/jccriado/matchingtools/issues/25/events","html_url":"https://github.com/jccriado/matchingtools/issues/25","id":347631482,"node_id":"MDU6SXNzdWUzNDc2MzE0ODI=","number":25,"title":"Treat replace single field case differently in Rule.apply","user":{"login":"jccriado","id":19803363,"node_id":"MDQ6VXNlcjE5ODAzMzYz","avatar_url":"https://avatars1.githubusercontent.com/u/19803363?v=4","gravatar_id":"","url":"https://api.github.com/users/jccriado","html_url":"https://github.com/jccriado","followers_url":"https://api.github.com/users/jccriado/followers","following_url":"https://api.github.com/users/jccriado/following{/other_user}","gists_url":"https://api.github.com/users/jccriado/gists{/gist_id}","starred_url":"https://api.github.com/users/jccriado/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/jccriado/subscriptions","organizations_url":"https://api.github.com/users/jccriado/orgs","repos_url":"https://api.github.com/users/jccriado/repos","events_url":"https://api.github.com/users/jccriado/events{/privacy}","received_events_url":"https://api.github.com/users/jccriado/received_events","type":"User","site_admin":false},"labels":[{"id":543646364,"node_id":"MDU6TGFiZWw1NDM2NDYzNjQ=","url":"https://api.github.com/repos/jccriado/matchingtools/labels/enhancement","name":"enhancement","color":"84b6eb","default":true},{"id":543646367,"node_id":"MDU6TGFiZWw1NDM2NDYzNjc=","url":"https://api.github.com/repos/jccriado/matchingtools/labels/question","name":"question","color":"cc317c","default":true}],"state":"open","locked":false,"assignee":null,"assignees":[],"milestone":null,"comments":0,"created_at":"2018-08-04T16:39:36Z","updated_at":"2018-08-04T16:39:36Z","closed_at":null,"author_association":"OWNER","body":"It would be natural (and useful for implementing #22) for rules of the type `field -> replacement` to be able to replace inside derivatives too. For example:\r\n```\r\nD(mu, D(nu, field)) /. field -> replacement = D(mu, D(nu, replacement))\r\n```\r\nThis functionality is already implemented in `eomsolutions.EOMSolution` (and it uses `Rule`s internally) so this issue's proposal is to move this to `Rule`.\r\n\r\nIt remains to decide whether it should be a new method of `Rule` (1) or considered as case inside `Rule.apply` (2). Option 1 seems to be better because it separates different behaviour in different functions, but option 2 has the advantage of being the behaviour a user would probably expect when supplying a `field -> replacement` rule."}}
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