@Fmbalbuena
┌─┼──┐     ┌┌┌┌
2 {⍵ ⍺+⍺} {⍵÷2}

@Fmbalbuena
SYNTAX ERROR
      ('^(.+).*\1$'⎕S)'input textinput tex'
                   ∧

@Fmbalbuena
┌┐
││
└┘

@Adám
2
0

@Fmbalbuena
DOMAIN ERROR
      (÷@⍳3)3 1 4 1 5
        ∧

@Adám
┌───┬───┬───┬───┬───┬───┬───┬───┐
│HEY│HEy│HeY│Hey│hEY│hEy│heY│hey│
└───┴───┴───┴───┴───┴───┴───┴───┘

@Adám
┌───┬───┐
│hey│heY│
├───┼───┤
│hEy│hEY│
└───┴───┘
┌───┬───┐
│Hey│HeY│
├───┼───┤
│HEy│HEY│
└───┴───┘

21	is the syntax identifier for "character constant"
19	is the syntax identifier for "primitive"
3	is the syntax identifier for "white space"
34	is the syntax identifier for "local name"
7	is the syntax identifier for "global name"
23	is the syntax identifier for "idiom"

 SC←{
     (n c)←2 3⊃¨⊂↓⍉201⌶⍬
     i←n∘⍳¨200⌶src
     ∊¨i{'<span class="',(¯4↓3↓⎕XML 0 '_'(⍺⊃c)),'">',⍵,'</class>'}¨¨⍵
 }
      ↑SC 'foo←{' '⍵ ⍵' '}'
<span class="MINI_DFNNAME">f</class><span class="MINI_DFNNAME">o</class><span class="MINI_DFNNAME">o</class><span class="MINI_PRIMITIVE">←</class><span class="{">{</class>
<span class="MINI_META">⍵</class><span class="MINI_WHITE"> </class><span class="MINI_META">⍵</class>
<span class="}">}</class>

@Fmbalbuena
2
2

      X←2 4 7 ⋄ Y←5 7 8 1
      (↓(0=X∘.|Y)){⍺⍵}Y
┌─────────────────────────┬───────┐
│┌───────┬───────┬───────┐│5 7 8 1│
││0 0 1 0│0 0 1 0│0 1 0 0││       │
│└───────┴───────┴───────┘│       │
└─────────────────────────┴───────┘
      (↓(0=X∘.|Y)){⍺⍵}¨Y
LENGTH ERROR
      (↓(0=X∘.|Y)){⍺ ⍵}¨Y
                       ∧
      (↓(0=X∘.|Y)){⍺⍵}¨⊂Y
┌─────────────────┬─────────────────┬─────────────────┐
│┌───────┬───────┐│┌───────┬───────┐│┌───────┬───────┐│
││0 0 1 0│5 7 8 1│││0 0 1 0│5 7 8 1│││0 1 0 0│5 7 8 1││