:. Obverse

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Obverse u :. v mu lu ru

The result of u :. v is the verb u,but with an assigned obverse v (used as the “inverse” under the conjunctions &. and ^:).

For example:

 y=: _4 0 4 3j4
 rp=: <@(%: , -@%:)"0 NB. Root pairs
 rp y
+--------+---+----+---------+
|0j2 0j_2|0 0|2 _2|2j1 _2j_1|
+--------+---+----+---------+
 I=: ^: _1
 rp I NB. No assigned obverse
rp^:_1
 rp I rp y
|domain error
| rp I rp y
 inv=: *:@{.@,@>
 inv rp y
_4 0 4 3j4
 RP=: rp :. inv NB. Assigned obverse in RP
 RP I RP y
_4 0 4 3j4
 rc=: <@(,: +)@(, -)@%:"0 NB. Root companions
 rc y
+---------+---+----+----------+
| 0j2 0j_2|0 0|2 _2| 2j1 _2j_1|
|0j_2 0j2|0 0|2 _2|2j_1 _2j1|
+---------+---+----+----------+
 RC=: rc :. inv
 RC I RC y
_4 0 4 3j4

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