Here are all three sections together, with Sections 1 and 2 included and polished.

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1. Substitutional Word Coding

Idea

Translating sentence maps where each word is replaced by a code word or symbol according to a fixed substitution table.

Rule

Compare coded and decoded sentences to identify common words.

• Each word maps to exactly one code.
• A common word in two sentences corresponds to the common code.
• Remove known mappings to identify the remaining ones.
• Use the completed mapping to decode or encode new sentences.

Example

Problem

If

• “sky blue water” is coded as “jo ne pa”
• “blue grass” is coded as “ne ka”

Decode “jo ka”.

Solution

Step 1: Compare the two sentences.

The word blue appears in both sentences.

The common code is ne.

Therefore,

blue → ne

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Step 2: Remove the known mapping.

From

sky blue water → jo ne pa

Since

blue → ne

the remaining mappings are

sky → jo
water → pa

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Step 3: Use the second sentence.

blue grass → ne ka

Since

blue → ne

the remaining word is

grass → ka

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Step 4: Decode the given code.

jo → sky
ka → grass

Therefore,

jo ka = sky grass

Answer

sky grass

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2. Letter Shift Cipher Decoding

Idea

Decoding messages where every letter has been shifted by a fixed number of positions in the alphabet (Caesar Cipher).

Rule

• Shift +n means every letter moves forward by n positions.
• To decode, move every letter backward by n positions.
• Wrap around the alphabet when necessary (A follows Z).

Example

Problem

Decode the ciphertext

KHOOR

using a Caesar shift of +3.

Solution

Step 1: Since the message was shifted forward by 3, decode by shifting every letter backward by 3.

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Step 2: Decode each letter.

K → H
H → E
O → L
O → L
R → O

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Step 3: Combine the letters.

H E L L O

Answer

HELLO

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3. Conditional Logic Decoders

Idea

Evaluating multi-rule encryption systems where the encoding method depends on conditions such as word length, vowel presence, or position.

Rule

Apply the rules in order.

1. If the word has more than 3 letters, reverse the word.
2. If the resulting word ends with a vowel, append “X”.
3. If a rule does not apply, leave the word unchanged.

Example

Problem

Apply these rules:

1. Reverse the word if its length is greater than 3.
2. If the reversed word ends with a vowel, add “X”.

Encode TAKE and IDEA.

Solution

Step 1: Encode “TAKE”

The word has 4 letters (>3), so reverse it.

TAKE → EKAT

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Step 2

Check whether EKAT ends with a vowel.

It ends with T, so Rule 2 does not apply.

Final code:

TAKE → EKAT

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Step 3: Encode “IDEA”

The word has 4 letters (>3), so reverse it.

IDEA → AEDI

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Step 4

AEDI ends with I, which is a vowel.

Append X.

AEDI → AEDIX

Answer

TAKE → EKAT
IDEA → AEDIX

These three sections are now complete, consistent, and formatted uniformly.