All in One!

To dear learners,

For you not to make unnecessary mistakes.

At one In accord or unity.
One and all Everyone.
One by one Individually in succession.

One by one

Adv. 1. one by one - in single file; “the prisoners came out one by one”
one after another, one at a time

  1. one by one - one piece at a time; “she sold the plates by the piece”
    by the piece

  2. one by one - apart from others; “taken individually, the rooms were, in fact, square”; “the fine points are treated singly”
    individually, on an individual basis, separately, severally, singly

One-to-one
adj

  1. (of two or more things) corresponding exactly

  2. denoting a relationship or encounter in which someone is involved with only one other person one-to-one tuition

  3. (Mathematics) Maths characterized by or involving the pairing of each member of one set with only one member of another set, without remainder
    n
    a conversation, encounter, or relationship between two people
    [b]

One-on-one [/b]
adj.

  1. Consisting of or being direct communication or exchange between two people: one-on-one instruction.

  2. Sports Playing directly or exclusively against a single opponent.

Hasta la vista!